Might Migrating Birds Have Infected The Svalbard Arctic Fox With Parasites?

The cat is the main host for Toxoplasma and spreads the infection in its droppings. Previous research has shown that isolated island groups without cats are in reality free of the parasite. Man can also be infected by eating meat from infected animals, and it can be transmitted to the embryo and deform it if the mother is infected while pregnant.

In her doctoral thesis, Kristin Wear Prestrud studied the distribution of the parasite in different animal species on Svalbard, and looked at the relationships with Toxoplasma strains in other parts of the world. Antibodies to Toxoplasma were found in the blood of the Arctic fox, polar bear, walrus, Svalbard reindeer, the sibling vole and several avian species.

Forty-three percent of the Arctic foxes sampled bore antibodies to the parasite. The incidence in polar bears was also high, and in walrus somewhat lower. Of avian species, the barnacle goose was the most common at 7% positive. The high incidence in Arctic foxes and polar bears was unexpected, because cats are forbidden on Svalbard and the only cats on the archipelago are some illegal ones at Barentsburg.

Kristin Wear Prestrud showed in her doctoral thesis that migratory birds are a probable source of infection for the parasite Toxoplasma gondii on Svalbard (the Spitsbergen archipelago), which has then infected the Arctic fox population, among other animals. The parasite can infect all animals and birds, including man, and normally produces few symptoms. It may, however, lead to the disease of toxoplasmosis, and over the years several Arctic foxes have been found dead from this infection on Svalbard.

In her thesis, Prestrud described migrating birds as a possible route of infection of Toxoplasma in the Arctic fox population on Svalbard. Genetic analyses showed that the parasite on Svalbard is identical to the most common Toxoplasma strains one finds in Europe, which supports the idea of a European source of infection on Svalbard.

Several bird species that breed on Svalbard overwinter in the more populated parts of Europe, where they might become infected. Geese, which graze on cultivated land during their migration, are especially suspect, and are a preferred prey of the Arctic fox during the summer. Transmission from mother to unborn offspring in the uterus may be significant for the Arctic fox, but probably not in polar bears, and it is likely that the level of infection in the fox and polar bear populations is also maintained by the animals eating their own species, which primarily occurs during the wintertime when available food is scarce.

Kristin W. Prestrud defended her thesis for the degree of Ph. D. at the Norwegian School of Veterinary Science, with the title "Toxoplasma gondii in the high arctic archipelago of Svalbard", on October 28, 2008.